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ThirdParty/assimp/code/PostProcessing/GenFaceNormalsProcess.cpp

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+/*
+---------------------------------------------------------------------------
+Open Asset Import Library (assimp)
+---------------------------------------------------------------------------
+
+Copyright (c) 2006-2025, assimp team
+
+All rights reserved.
+
+Redistribution and use of this software in source and binary forms,
+with or without modification, are permitted provided that the following
+conditions are met:
+
+* Redistributions of source code must retain the above
+  copyright notice, this list of conditions and the
+  following disclaimer.
+
+* Redistributions in binary form must reproduce the above
+  copyright notice, this list of conditions and the
+  following disclaimer in the documentation and/or other
+  materials provided with the distribution.
+
+* Neither the name of the assimp team, nor the names of its
+  contributors may be used to endorse or promote products
+  derived from this software without specific prior
+  written permission of the assimp team.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+---------------------------------------------------------------------------
+*/
+
+/**
+ * @file Implementation of the post-processing step to generate face
+ * normals for all imported faces.
+ */
+
+#include "GenFaceNormalsProcess.h"
+#include <assimp/Exceptional.h>
+#include <assimp/postprocess.h>
+#include <assimp/qnan.h>
+#include <assimp/scene.h>
+#include <assimp/DefaultLogger.hpp>
+
+using namespace Assimp;
+
+// ------------------------------------------------------------------------------------------------
+// Returns whether the processing step is in the given flag field.
+bool GenFaceNormalsProcess::IsActive(unsigned int pFlags) const {
+    force_ = (pFlags & aiProcess_ForceGenNormals) != 0;
+    flippedWindingOrder_ = (pFlags & aiProcess_FlipWindingOrder) != 0;
+    leftHanded_ = (pFlags & aiProcess_MakeLeftHanded) != 0;
+    return (pFlags & aiProcess_GenNormals) != 0;
+}
+
+// ------------------------------------------------------------------------------------------------
+// Executes the post-processing step on the given imported data.
+void GenFaceNormalsProcess::Execute(aiScene *pScene) {
+    ASSIMP_LOG_DEBUG("GenFaceNormalsProcess begin");
+
+    if (pScene->mFlags & AI_SCENE_FLAGS_NON_VERBOSE_FORMAT) {
+        throw DeadlyImportError("Post-processing order mismatch: expecting pseudo-indexed (\"verbose\") vertices here");
+    }
+
+    bool bHas = false;
+    for (unsigned int a = 0; a < pScene->mNumMeshes; a++) {
+        if (this->GenMeshFaceNormals(pScene->mMeshes[a])) {
+            bHas = true;
+        }
+    }
+    if (bHas) {
+        ASSIMP_LOG_INFO("GenFaceNormalsProcess finished. "
+                        "Face normals have been calculated");
+    } else {
+        ASSIMP_LOG_DEBUG("GenFaceNormalsProcess finished. "
+                         "Normals are already there");
+    }
+}
+
+// ------------------------------------------------------------------------------------------------
+// Executes the post-processing step on the given imported data.
+bool GenFaceNormalsProcess::GenMeshFaceNormals(aiMesh *pMesh) {
+    if (nullptr != pMesh->mNormals) {
+        if (force_) {
+            delete[] pMesh->mNormals;
+        } else {
+            return false;
+        }
+    }
+
+    // If the mesh consists of lines and/or points but not of
+    // triangles or higher-order polygons the normal vectors
+    // are undefined.
+    if (!(pMesh->mPrimitiveTypes & (aiPrimitiveType_TRIANGLE | aiPrimitiveType_POLYGON))) {
+        ASSIMP_LOG_INFO("Normal vectors are undefined for line and point meshes");
+        return false;
+    }
+
+    // allocate an array to hold the output normals
+    std::vector<aiVector3D> normals;
+    normals.resize(pMesh->mNumVertices);
+
+    // mask to indicate if a vertex was already referenced and needs to be duplicated
+    std::vector<bool> alreadyReferenced;
+    alreadyReferenced.resize(pMesh->mNumVertices, false);
+    std::vector<aiVector3D> duplicatedVertices;
+
+    auto storeNormalSplitVertex = [&](unsigned int index, const aiVector3D& normal) {
+        if (!alreadyReferenced[index]) {
+            normals[index]           = normal;
+            alreadyReferenced[index] = true;
+        } else {
+            duplicatedVertices.push_back(pMesh->mVertices[index]);
+            normals.push_back(normal);
+            index = pMesh->mNumVertices + static_cast<unsigned int>(duplicatedVertices.size() - 1);
+        }
+        return index;
+    };
+
+    const aiVector3D undefinedNormal = aiVector3D(get_qnan());
+
+    // iterate through all faces and compute per-face normals but store them per-vertex.
+    for (unsigned int a = 0; a < pMesh->mNumFaces; a++) {
+        const aiFace &face = pMesh->mFaces[a];
+        if (face.mNumIndices < 3) {
+            // either a point or a line -> no well-defined normal vector
+            for (unsigned int i = 0; i < face.mNumIndices; ++i) {
+                face.mIndices[i] = storeNormalSplitVertex(face.mIndices[i], undefinedNormal);
+            }
+            continue;
+        }
+
+        const aiVector3D *pV1 = &pMesh->mVertices[face.mIndices[0]];
+        const aiVector3D *pV2 = &pMesh->mVertices[face.mIndices[1]];
+        const aiVector3D *pV3 = &pMesh->mVertices[face.mIndices[face.mNumIndices - 1]];
+        // Boolean XOR - if either but not both of these flags are set, then the winding order has
+        // changed and the cross-product to calculate the normal needs to be reversed
+        if (flippedWindingOrder_ != leftHanded_)
+            std::swap(pV2, pV3);
+        const aiVector3D vNor = ((*pV2 - *pV1) ^ (*pV3 - *pV1)).NormalizeSafe();
+
+        for (unsigned int i = 0; i < face.mNumIndices; ++i) {
+            face.mIndices[i] = storeNormalSplitVertex(face.mIndices[i], vNor);
+        }
+    }
+
+    // store normals (and additional vertices) back into the mesh
+    if (!duplicatedVertices.empty()) {
+        const aiVector3D * oldVertices = pMesh->mVertices;
+        auto oldNumVertices = pMesh->mNumVertices;
+        pMesh->mNumVertices += static_cast<unsigned int>(duplicatedVertices.size());
+        pMesh->mVertices = new aiVector3D[pMesh->mNumVertices];
+        memcpy(pMesh->mVertices, oldVertices, oldNumVertices * sizeof(aiVector3D));
+        memcpy(pMesh->mVertices + oldNumVertices, duplicatedVertices.data(), duplicatedVertices.size() * sizeof(aiVector3D));
+        delete[] oldVertices;
+    }
+    pMesh->mNormals = new aiVector3D[pMesh->mNumVertices];
+    memcpy(pMesh->mNormals, normals.data(), normals.size() * sizeof(aiVector3D));
+
+    return true;
+}